Chemistry – Module 1 – The Chemical Earth

1. The living and nonliving components of Earth contain mixtures

construct word and balanced equations of chemical reactions as they are encountered

General Reactions

a) Single displacement reaction: EG: Fe(s) + 2HCl(aq) FeCl2 (aq) + H2 (g)

b) Double displacement reaction: EG: AgNO3 (aq) + NaCl(aq) AgCl (s) + NaNO3 (aq)

c) Combination reaction: EG: 2Mg(s) + 02 (g) 2Mg0(s)

d) Decomposition reaction: Heating Visible light or UV Electrolysis

Common Reactions

a) Metal + Acid Salt + Hydrogen gas

b) Metal + Water Metal hydroxide + water

c) Metal + Salt New Salt + Metal

d) Acid + Base Salt + Water

e) Acid + Carbonate Salt + Carbon dioxide + water

f) Salt + salt New salts

g) Metal Oxide + water Acidh) Combustion

i. Element + Oxygen Element Oxide

ii. Hydrocarbon + Oxygen Carbon dioxide + Water

i) Heat + Carbonate Metal Oxide + Carbon Dioxide

Identify the difference between elements, compounds and mixtures in terms of the particle theory

1

All matter is made of continuously moving particles.

An element is a pure substance made up of only one type of atom. It cannot be broken down into smaller substances using ordinary physical and chemical means. All elements are homogeneous (means they have uniform composition throughout). Some elements include aluminium, copper, gold etc.

A compound contains two or more different elements chemically combined in a fixed ratio by mass. The compound’s properties are different from those of the elements that make it up A compound is a pure substance which can be decomposed into simpler substances, for example into elements. Compounds are homogeneous and also have definite melting and boiling points. Some common compounds include water, NaCl, sugar etc.

A mixture contains two or more types of particles in any proportion. They can be physically separated. The components of a mixture keep their own properties. A mixture contains 2 or more substances physically combined together in any given ratio.

Mixture Pure Substance

Can be separated into two or more pure substances by physical or mechanical means such as filtering, boiling or using a magnet.

Cannot be separated into two or more substances by physical or mechanical means.

May be homogenous or heterogenous Only homogenous

Displays properties of the pure substances that make it up. Different parts of a mixture may show different properties

Has properties such as appearance, colour, density, m.p. and b.p. which are constant.

Has properties that change as the ratio of substances is changed

Properties never change, no matter how it is prepared/ purified

Variable composition Fixed composition

2

identify that the biosphere, lithosphere, hydrosphere and atmosphere contain examples of mixtures of elements and compounds

Rank Biosphere Atmosphere Hydrosphere Lithosphere Living Matter1 Oxygen Nitrogen Oxygen Oxygen Oxygen2 Silicon Oxygen Hydrogen Silicon Carbon3 Aluminium Argon Chlorine Aluminium Hydrogen4 Iron Hydrogen Sodium Iron Nitrogen5 Calcium Carbon Magnesium Calcium Calcium

Table containing the most abundant elements in each sphere in decreasing order.

Most abundant non-metal: Oxygen

Most abundant metal: Aluminum

Most abundant semi-metal: Silicon

Atmosphere: It is a layer of gas about 200-300 km thick which surrounds the Earth. 75% of the mass of the atmosphere is in the lowest 15km. Various elements exist in the atmosphere including: Nitrogen, oxygen, hydrogen, helium, argon. Compounds include Methane, Carbon dioxide, Nitrogen dioxide, Water and Carbon monoxide. Mixtures include Pollen, dust, air, soot/ash etc.

Biosphere: The biosphere is a region of the Earth’s surface which is composed of all interacting ecosystems where organisms interact with the atmosphere, lithosphere, and hydrosphere resulting in a flow of energy and matter. Elements – Carbon, Oxygen, Nitrogen. Compounds – Water, Carbon dioxide, Sodium Chloride, Proteins, Carbohydrates, Aluminosilicates, carbon compounds, silicon dioxide etc. Mixtures include blood, soft drinks etc.

Hydrosphere: Layer that is discontinuous on Earth and consists of all of the Earth’s water. Elements are Hydrogen, oxygen and nitrogen. Compounds are all soluble substances including water, NaCl, Carbon dioxide, Phosphate etc. Mixtures include freshwater, salt water.

Matter

Homogeneous Heterogenous

Pure Substances Mixtures

Can be separated into

Can be separated

physically into

3

Elements Compounds

Lithosphere: Crust and the top part of the mantle. Elements include gold, silver, silicon. Compounds include all metal oxides, Aluminosilicates, hydrocarbons. Mixtures include rocks, soil, humus, various silicates etc.

Identify and describe procedures that can be used to spate naturally occurring mixtures of: Solids of different sizes, Solids and Liquids, Dissolved solids in liquids, Liquids, Gases.

Separation of solids of different sizes: In order sperate solids of different sized the most appropriate method is known as sieving. Sieving involves passing the mixture through a sieve which contains tiny holes that allow only substances of a particular size to pass through. Thus sieving relies on size. The smaller substance will pass through the sieve while the larger one will be trapped. Thus the mixture is separated.

Separating solids and liquids: There are two methods:1) Filtration. The solution is passed through a funnel which is lined with filter

paper. The liquid is able to pass through but the solid is caught in the filter.2) Sedimentation and decantation. The solids are allowed to settle to the

bottom of the container. Then the liquid is carefully poured off, leaving the solid at the bottom of the container.

Separating dissolved solids in liquids: There are two methods:1) Evaporating to dryness. This is done when the liquid is of no use and can

be disposed of. The solution is heated until all the liquid has evaporated leaving the solid behind.

2) Distillation. This is done when the liquid is desirable. The solution is placed in the apparatus and heated. The liquid evaporates and moves through tubing to another container. On the way the tube is cooled so that the gas is condensed causing it to change back to liquid state before ending up in a secondary container. The solid is left at the bottom of the first beaker. The liquid collected is called the distillate.

Separating Liquids: Again there are two methods:1) Fractional Distillation. The apparatus is slightly different to that of

distillation but the process is the same. The apparatus contains a fractionating column which consists of hundreds of glass beads. This arrangement allows for repeated condensations and evaporations, thus the solution is distilled 10-100 times. Liquid with the lowest b.p comes off first

2) Separating Funnel. Use if the liquids are immiscible (i.e. don’t dissolve in each other). The liquids are layered. One is allowed through the funnel and just before it finishes the valve is closed. Thus separating the liquids.

Two solids based on solubility: If one substance in a particular mixture is soluble in a certain substance while the other isn’t they can be separated. The solution is added, which dissolves one of the substances, and then one filtration is used to remove the insoluble substance, the remaining filtrate is dried to retrieve the other solid.

Separating Gases: Again two methods:

4

1) Fractional Distillation. Gases are condensed to liquid state then distil2) Differences in solubility. Gases are run through a series of “u” shaped

tubes each containing a substance that will dissolve a particular gas, thus leaving only the desired gas(es) at the end.

assess separation techniques for their suitability in separating examples of earth materials, identifying the differences in properties which enable these separations

Separation Method Property used in the separationSieving Particle sizeVaporization (Evap. To dryness) Liquid has lower m.p. than solidDistillation Big difference in b.p.Frac. Distillation Small but significant difference in m.p.Filtration One solid, one liquid/solutionUsing a separating funnel Two immiscible liquids Adding a solvent then filtration One substance is soluble in the chosen

solvent, while the others aren’t.

describe situations in which gravimetric analysis supplies useful data for chemists and other scientists

A gravimetric analysis is a technique employed to find the percentage proposition of a substance in a sample.

There are numerous situations where a gravimetric analysis may be used:o Used to decide whether a mineral deposit contains a high enough

percentage of a particular substance to be economically viable.o Also, to determine the composition of soil, for its suitable use in

crops and agriculture.o Also, to determine the percentage of substances in the air, soil or

water. This may be for pollution control/standards.o Furthermore, to ensure quality control of manufacture products

including things like insecticideso Analysis of molten mixtures of metals to ensure that the alloys

formed are of a desired compositiono Lastly, to analyse alcohol content in drinks and also for the analysis

of blood to check for alcohol – BAC

apply systematic naming of inorganic compounds as they are introduced in the laboratory

Binary ionic compounds – the metal is named first, then the non-metal. The last few letters of the non-metal are replaced with the suffix “-ide”, e.g. oxygen oxide. Example AgCl = Silver Chloride

Ionic compounds with a polyatomic ion – The metal is named first, then the radical. The radical is treated as a single ion. NaNO3 = Sodium Nitrate

Covalent molecular substances – The element higher up in the periodic table is named first. Prefixes (mono, di, tri, tetra etc) are used to indicate the number of atoms of each element. Eg – Cl2O7 = Dichlorine heptoxide, NO2 – Nitrogen Dioxide (there is no need to write mononitrogen dioxide)

5

identify IUPAC names for carbon compounds as they are encountered

Series Name Ending General Formula Bonding in C SeriesAlkane -ane CnH2n+2 Single (C-C)Alkene -ene CnH2n Double (C=C)Alkyne -yne CnH2n-2 Triple (CΞC)

In order to name a hydrocarbon, five steps must be followed:1. Look for the longest carbon chain. (Note chain may be bent or circular)2. Identify whether it is an alkane, alkene or alkyne and also name the bond

number. E.g. 2-heptyne etc. If there is more than one double or triple bond a appropriate prefix is attached to the name. Eg: 1,2-dioctene. This shows us that there is a double bond at both the 1st and 2nd carbon atoms.

3. Look for any alkyl groups – Eg methyl, ethyl, etc. Then name these according to the bond number and also the number of alkyl groups. For example: 5,6,7-trimethyl 2-octene. The 5,6,7 show which number of carbon atom the methyl is attached to. The tri indicates there are three methyl’s in total and the 6 indicates that the double bond is located on the 6th carbon atom. Another example: 7 ethyl 4,5 methyl octane (Always name in alphabetical order, while ignoring the numbers). This shows us that at the 4th and 5th carbon atoms there is the methyl alkyl group while at the 7th carbon atom there is an ethyl

4. Look for any other elements present (called halogens) in the chain. Eg: chlorine or bromine etc. These are also named to the number of carbon atom that they are attached to. For example: 3-chloro pentane means that at the 3rd carbon atom there is an atom of chlorine. There are orders of preferences if two or more of all the previous things are present. Always name the substances in each group alphabetically.

1) The double triple bonds (look at the smallest number and use this as a guideline for everything else)

2) Halogens – in alphabetical order3) Alkyl groups – also in alphabetical order

NOTE: If the carbon chain is circular. It is known as a cyclic hydrocarbon. For example if pentane was drawn as a circular chain it would be known as cyclopentane. All of the other rules apply as per normal.

NOTE: An isomer is a substance that has the same molecular formula to that of another substance. It however has a different structural formula, different physical properties and slightly different chemical properties.

6

2. Although most elements are found in combinations on Earth, some elements are found uncombined

explain the relationship between the reactivity of an element and the likelihood of its existing as an uncombined element

The reactivity of a element will emphasise the likelihood of it existing as an uncombined element. The more reactive the element the less likely it is to occur uncombined. The opposite is true for unreactive elements which are more likely to occur uncombined in nature. Most elements are unstable and therefore are reactive.

For example: the most reactive metal – Francium and the most reactive non-metal – Fluorine are the least likely of all the elements to exist solely on their own. On the other hand the least reactive elements – the noble gases – occur in nature uncombined. For example helium and argon exist uncombined in the atmosphere. All elements react to try to achieve noble gas configuration – which is a state of no reactivity. All the reactions occur because the elements want to become as stable as the noble gases.

Metals Semi-Metals Non-metals

Shiny + Solid (room temp) Low sheen Dull

Highly malleable and ductile Moderately malleable and ductile Brittle and inelastic

Conducts electricity Semi-conductor Electrical insulator

Conducts heat Conducts heat Heat insulator

Low electronegativity Variable electronegativity High electronegativity

Higher boiling point Variable boiling points Low boiling point

classify elements as metals, non-metals and semi-metals according to their physical properties

Note: of the naturally occurring elements, at room temperature:

- two are liquids: mercury (metal) and bromine (non-metal)

7

- eleven are gases: oxygen, nitrogen, fluorine, chlorine, hydrogen, helium, argon, xenon, krypton, neon, radon (all non-metals)

- the rest are solids

account for the uses of metals and non-metals in terms of their physical properties

The physical properties most commonly involved are the melting point, density, electrical conductivity, hardness and tensile strength.

Some examples of where metals are used because of their physical properties:- Aluminium is used for making aircrafts primarily because of

its low density (combined with adequate mechanical strength)- Iron is used to make motor cars and trains because it has high tensile

strength.- Copper is used for electrical wiring in houses and other buildings because of

its high electrical conductivity. However, for high voltage transmission lines aluminium is preferred because it has a lower density and the mass of cables is important in this scenario

- Tungsten is used for filaments in electrical light bulbs because of its extremely high melting point.

- Aluminium is also used to make cans and aluminium foil for wrapping food. This is because it is a durable metal, very malleable, can be rolled into thin sheets and is insoluble in water.

- Gold is used in jewelry and computer parts because of its good electrical conductivity, its malleability, it is ductile, lustrous and attractive

- Silver is also used in jewelry but is also used in electronics because it a superconductor of electricity, malleable and ductile.

Some examples where non-metals are used based on their physical properties:- Carbon as graphite is used as electrodes in common dry cells because of its

significant electrical conductivity and as a dry lubricant because of its slippery nature

- Carbon also in the form of diamond is used for jewelry because of its supreme hardness, resistance to scratching and also because it has a high light refractive index.

- Nitrogen in liquid state is used as a cooling agent because of the suitability of its melting and freezing points.

- Helium is used for filling balloons because its an inert gas and has a very low density which makes the balloons float in the air.

- Neon is used in light sensitive switches because it is an unreactive gas which emits red light when electricity is passed through it.

- Diamond (a form of carbon) is used in cutting tools as it has a strong covalent network, making it one of the hardest substances on Earth.

8

3. Elements in Earth materials are present mostly as compounds because of interactions at the atomic level

• identify that matter is made of particles that are continuously moving and interacting

According to the particle theory, all matter is made up of small particles that are continuously moving. In solids the particles vibrate. In liquids there is translational and vibrational motion. In gases there is rapid translational motion of particles. In solids the particles are arranged in a very orderly manner. In a liquid there is less orderly arrangement of particles. In a gas, however, the particles are well separated by space.

describe qualitatively the energy levels of electrons in atoms

Electrons have a -1 charge. They are written e-. There are the same number of electrons as there are protons in an atom. This is in order to balance the charge of an atom. Electrons rotate around the nucleus of an atom in what is known as an electron cloud. There are a number of subshells in which the electrons rotate. The order of these subshells is known as “SPDFGH”. Electrons in atoms have discrete energy levels which are called 1st, 2nd, 3rd level and so on. Electrons in each level have a distinct and constant amount of energy. Energy levels increase as the amount of electrons and shells increase. I.e. electrons in higher levels will have more energy than that of lower levels. The maximum number of electrons orbiting in the nth shell is 2n2.

describe atoms in terms of mass number and atomic number

Mass Number = Number of protons + number of neutronsAtomic Number = Number of protons = Number of electrons

Eg: Calcium – Na

Mass number = 40Atomic number = 20

Therefore number of protons = 20, neutrons = 20, electrons = 20.

Note: The mass number can also be known as the sum of the mass of the protons, neutrons and electrons, under the assumption that neutrons and protons weigh 1 unit each, and that electrons are significantly lighter (therefore they are not included in the calculations above. Electrons are 1/2000 of a proton in mass.

describe the formation of ions in terms of atoms gaining or losing electrons

Electrons in the outermost shell are in the valence shell and thus are known as valence electrons. Whether an atom loses or gains electrons depends on the amount of valence electrons. Except for hydrogen and helium, if an atom has 1,2

9

or 3 electrons in its valence shell it will lose those electrons to form an cation (positively charged ion). If the atom has 5,6 or 7 valence it will gain electrons in order to become an anion (negatively charged electron). If the atom has 4 electrons it can either gain or lose those electrons. Hydrogen can gain or lose one electron to hydrogen ion. Thus the valence electrons determine whether atoms gain/lose electrons (i.e. whether they become anions or cations)Note: Between a metal and a non-metal, electrons are transferred, forming ions on both sides. Because of this sudden gain/loss in electrons, the ions are negatively and positively charged, respectively, and therefore bond through electrostatic attraction, in a process called ionic bonding. In semi-metals and non-metals, the sharing of electrons will yield a stable electron configuration, in a process called covalent bonding.

apply the Periodic Table to predict the ions formed by atoms of metals and non-metals

Group I (alkali metals) generally tend to lose one electron, forming a positively charged ion of +1 charge.

Group II (alkali-earth metals) generally tend to lose two electrons, forming a positively charged ion of +2 charge.

Group IV (halogens) generally tend to gain 1 atom and form a negatively charged ion of -1 charge.

Metals generally form positive ions while non-metals form negative ions.

describe the formation of ionic compounds in terms of the attraction of ions of opposite charge

Ionic compounds consist of positively charged ions (cations) and negatively charged ions (anions) held together by electrostatic attraction. These two ions may bond infinitely, so it is much more practical to represent these in their empirical formulae.

Positive and negative ions attract one another very strongly and so ionic compounds consist of interlocking lattices or arrays of positive and negative ions. The strong attractive forces that hold these ions together in a crystal lattice are called ionic bonding.

describe molecules as particles which can move independently of each other

Molecules are particles that may move independently of each other. The forces that hold the molecules together are known as intermolecular forces. If these forces are weak the molecules may move independently of each other. However if these forces are extremely strong the molecules maybe tightly bound and their movement maybe restricted to just vibrations.

Molecules are made up of several atoms joined together, although some single atoms (noble gases) may exist as mono-atomic molecules.

10

Atoms that share electrons (non-metals) obtain a stable electron configuration and can therefore exist as diatomic molecules. Eg O2 ,H2

distinguish between molecules containing one atom (the noble gases) and molecules with more than one atom

Molecules containing one atom are called monatomic molecules (one atom in the molecule). Only the noble gases are able to achieve this molecular structure due to the fact that they are extremely stable and don’t react.

Other elements on the other hand cannot be in a monatomic molecular structure. They will be at least in diatomic structure. For example O2 ,H2. These diatomic molecules are able to exist by themselves in nature. Only non-metals are able to be seen in this diatomic state in nature. This is because metals will usually form oxides or will be in a large metallic or lattical structure which consists of millions of atoms infinitely bonded.

Other elements may form compounds which contain two or more different elements in each compound. For example H2O. In this case the molecule contains 2 hydrogen atom and one oxygen atom.

describe the formation of covalent molecules in terms of sharing of electrons

When atoms share electron pairs the type of bonding formed is known as a covalent bond. Covalent bonds occur when a non-metal, combines with another non-metal. The intramolecular forces in a covalent molecule are extremely strong

There are three types of covalent bonds:

Single – Each atom shares one pair of electrons.Double – Each atom shares two pairs of electrons.Triple – Each atom shares three pairs of electrons.

Covalent bonds can be polar (atoms sharing electrons are different. Eg. HCl) or can be non-polar (atoms sharing electrons are the same Eg. O2). The atom that attracts the electrons more strongly is said to be more electronegative

Molecules can be polar or non-polar depending on whether their bonds are polar or non-polar and also on their shape. A molecule can have polar bonds and yet be non-polar if the bonds cancel out so that there is no net dipole (charge)

Intermolecular forces determine the physical properties of covalent molecular substances. There are three main types of intermolecular forces: dispersion forces, dipole-dipole forces and hydrogen bonds.

Dispersion forces: - these are very weak, induced, temporary forces of attraction, which exist between all molecules due to constantly moving electron clouds.

Dipole-Dipole forces: - are permanent electrostatic attractions between the positive and negative ends of polar molecules caused by uneven distribution of electrons within the molecule

Hydrogen bonds: - are strong attractive forces between a hydrogen atom and an atom of fluorine, oxygen or nitrogen in a nearby molecule.

11

Covalent bonds can give rise to two types of structures:1) Covalent Molecular2) Covalent Network

Covalently bonded substances DO NOT conduct electricity (except graphite) in the solid or liquid states, because they are unchanged and also because there are no mobile electrons present.

All bonding electrons are tightly locked in covalent bonds.

12

4. Energy is required to extract elements from their naturally occurring sources

identify the differences between physical and chemical change in terms of rearrangement of particles

In a physical change the intermolecular bonds (which are fairly weak) are broken. In a physical change no new substances are formed, rather the substance changes its state. For example water boiling.

In this example there are no new substances formed and thus there is no rearrangement of particles within molecules. Rather energy is provided to the molecules via the heat which causes them to have enough energy to separate themselves from one another (i.e. the intermolecular bonds are broken). The result is that some water particles leave the surface of the liquid (can be seen when the water evaporates).

In a physical change the energy change is relatively small. Also a physical change is easy to reverse (condensation of water). In a physical change there are mass changes. (I.e. the mass of the substance will change after a physical change).

In a chemical change however the intramolecular bonds (which are relatively strong) are broken. In a chemical change, new substances are formed. An example of this can be seen during the electrolysis of water.

In this example, two new substances, O2 and H2 are formed. Thus there is a clear rearrangement of particles. In electrolysis, there is a lot more energy provided to the water molecules, enough energy is provided to break the intramolecular bonds between the hydrogen and the oxygen.

In the apparatus the negative oxygen ions are attracted to the positively charged cathode where as the positive hydrogen ions are attracted to the negatively charged cathode. Thus electrolysis proved enough energy to split intramolecular bonds, causing the re-arrangement of particles to form two new substances.

A chemical change is difficult to reverse, has high energy changes and the overall mass of the substance is conserved.

13

Boiling Electrolysis Physical Change Breaks intermolecular forces Changes physical state (liquid to gas) Relatively low amount of energy

needed No new substances formed

Chemical change Breaks intramolecular forces Relatively large amount of energy

needed New substances formed (H2 and O2)

Summarise the difference between the boiling and electrolysis of water as an example of the difference between physical and chemical changes

identify light, heat and electricity as the common forms of energy that may be released or absorbed during the decomposition or synthesis of substances and identify examples of these changes occurring in everyday life

Decomposition is the breaking down of compounds into simpler substances.

Heat, light and electricity are common forms of energy released or absorbed during various synthesis and decomposition reactions.

Heat may be absorbed or released in endothermic and exothermic reactions, respectively.

Example Method used Energy absorbed or releasedProduction of metals from their ores. Eg. Copper from copper carbonate

Heat in furnace Heat energy is absorbed by the copper carbonate, resulting in decomposition

Production of aluminium from aluminium oxide (in bauxite)

Pass electricity through molten aluminium oxide

Electrical energy is absorbed

Development of film Action of sunlight on silver bromide (film)

Solar energy (light) is used to decompose silver bromide.

The combustion of magnesium

( )

Burn magnesium in air Results in a brilliant light and considerable amounts of heat being released.

Synthesis is the joining of simpler substances to form more complex substances through chemical reactions.

Example Method used Energy absorbed or releasedThe rusting of iron Iron reacts with oxygen in the air,

in the presence of water to form iron (III) oxide

Energy released in the form of heat

Photosynthesis Carbon dioxide and water combine to form glucose and oxygen

Light energy is absorbed and heat energy is released

Formation of nitrogen oxides in the atmosphere

Lighting causes atmospheric nitrogen to combine with oxygen to form nitrogen monoxide

Electrical energy is absorbed

Burning of coal or coke to produce electricity or to make steel

Coal is heated in furnaces Heat energy is absorbed to the start the reaction. Heat energy is also produced.

14

explain that the amount of energy needed to separate atoms in a compound is an indication of the strength of the attraction, or bond, between them.

The amount of energy needed to decompose chemical compounds and mixtures is indicative of the strength of the bonds. Stronger bonds require more energy to break them, a prominent example being the difference between boiling water and electrolysis. Another example is that mercury oxide can be easily decomposed by heating whereas potassium oxide cannot. This indicates that the potassium is more reactive than the mercury so it forms a stronger intramolecular attraction. Therefore more energy is required to overcome the strong attraction between atoms.

Intramolecular bonds are very strong and therefore require more energy to break than intermolecular bonds. This can be seen in example of the boiling/electrolysis of water. Heat energy is enough to break the intermolecular bonds to cause the change of state, but electrical energy is needed to break the intramolecular bonds to create two new substances.

5. The properties of elements and compounds are determined by their bonding and structure

15

identify differences between physical and chemical properties of elements, compounds and mixtures

Mixture Compound Element

Can be separated into two or more pure substances by physical or mechanical means such as filtering, boiling or using a magnet.

Cannot be separated into two or more substances by physical or mechanical means. But can be decomposed through chemical means.

Cannot be decomposed through any means

May be homogenous or heterogenous

Only homogenous Only homogenous

Displays properties of the pure substances that make it up. Different parts of a mixture may show different properties

Has properties such as appearance, colour, density, m.p. and b.p. which are constant.

Has properties such as appearance, colour, density, m.p. and b.p. which are constant.

Has properties that change as the ratio of substances is changed

Properties never change, no matter how it is prepared/ purified

Properties never change, no matter how it is prepared/ purified

Variable composition Fixed composition --------------------------------

Indefinite melting and boiling points

Definite melting and boiling points

Definite melting and boiling points

describe the physical properties used to classify compounds as ionic or covalent molecular or covalent network

Properties of ionic substances –

solids at room temperature high melting and high boiling points due to strong intramolecular bonds,

through electrostatic attractions. Also because there is strong ionic bonding extending throughout the lattice

hard because the ions are strongly bound in the lattice brittle because distortion causes repulsion between ions of like charges as solids they do not conduct electricity because the ions are firmly bound

in the lattice, meaning no free ions to carry the charge. when molten or when in aqueous state they are able to conduct electricity

because there are free-moving ions able to carry an electrical charge.

Properties of covalent molecular substances –

16

at room temperature they are generally liquids or gases (few are solids), low melting/boiling points due to the fact they have very weak intermolecular bonds

when sold they are soft because of the weak forces between molecules don’t conduct electricity in either solid or liquid/aqueous state as there are

no charge carriers. Also because the molecules are uncharged and electrons are localized in covalent bonds or on the atoms)

in solutions they do not conduct electricity unless they actually react with water to form ions

Properties of covalent network substances –

non conductors when solid or molten since no free/moving electrons very high melting / boiling points because they are bonded in three

dimensions and strong covalent bonds extend throughout the lattice. hard because atoms are tightly bound in a lattice brittle because distortion breaks covalent bonds

distinguish between metallic, ionic and covalent bonds

17

Metallic bonding – In metallic bonding there is a lattice of positive ions surrounded by a sea of delocalised electrons.

Metals have some electrons that are very mobile and relatively free to move. Under the influence of a voltage they migrate towards the positive terminal. Therefore all metals are electrical conductors in the solid state.

The delocalised electrons are also responsible for the transmission of heat energy in metals

The delocalised electrons do not belong to any particular atom so the bonding is said to be non-directional. Therefore if sufficient force is applied to the metal, one layer of atoms can slide over another without disrupting the metallic bonding. Thus justifying the known property of metals being malleable.

As a result of their malleability metals can be hammered into sheets or drawn into wires (ductile). The high melting and boiling points of most metals is due to the strong electrostatic attraction between the positive metal ions and the mobile electrons.

Note: Group 2 metals release two electron per atoms to form STRONGER METALLIC bonds than group 1 metals and therefore have higher melting and boiling points.

Properties of metallic substances – Good conductors of heat and electricity because of the delocalised electron

transfer charge and thermal energy. High melting and boiling points because of the strong metallic bonding

extending throughout the lattice Dense because the ions are packed tightly in the lattice Malleable and ductile since distortion does not disrupt the metallic bonding Lustrous because the delocalised electrons cause the reflection of light

Ionic bonds are a result of two oppositely charged ions being bonded due to electrostatic attraction. Ionic bonds may conduct electricity in an aqueous state as there are free-moving ions able to carry an electrical charge.

A covalent bond joins two non-metals through the sharing of electrons. Because this bond is an intermolecular one, it is very weak and makes for a lower boiling and melting point.

describe metals as three-dimensional lattices of ions in a sea of electrons

18

In metallic bonding there is a lattice of positive ions surrounded by a sea of delocalised electrons.

Metals have some electrons that are very mobile and relatively free to move.

For more clarification look at the previous dot point on metallic bonding.

describe ionic compounds in terms of repeating three-dimensional lattices of ions

Ionic bonds are a result of two oppositely charged ions being bonded due to electrostatic attraction. Ionic bonds may conduct electricity in an aqueous state as there are free-moving ions able to carry an electrical charge.

NaCl

Ionic compounds consist of positively charged ions (cations) and negatively charged ions (anions) held together by electrostatic attraction. These two ions may bond infinitely, so it is much more practical to represent these in their empirical formulae.

Positive and negative ions attract one another very strongly and so ionic compounds consist of interlocking lattices or arrays of positive and negative ions. The strong attractive forces that hold these ions together in a crystal lattice are called ionic bonding.

explain why the formula for an ionic compound is an empirical formula

An empirical formula is a simplified ratio of elements in a compound. Eg NaCl which tells us that for every sodium atom there is one chlorine atom. Ionic compounds may infinitely bond, and because ionic compounds do not change properties, it is much more practical to represent them as an empirical formula. The empirical formula of an ionic compound indicates the kinds of atoms that are present in the compound as well as the relative number (ratio) of each kind of atom. An empirical formula is used since there are no discrete molecules in the

19

lattice of an ionic substance, so only an empirical formula can be used to express its composition.

identify common elements that exist as molecules or as covalent lattices

Covalent Molecular- All the diatomic gases such as oxygen, hydrogen, chlorine, fluorine

and nitrogen.- Bromine as a diatomic liquid and iodine as a diatomic solid.- Phosphorus and sulfur exist as covalent P4 and S8 covalent

molecules respectively

Covalent Lattices- Carbon exists as diamond which is a three-dimensional lattice and as

graphite which is a two-dimensional lattice- The semi-metals B, Si, Ge, As, Sb, and Te closely approximate to

covalent lattices though their bonding electrons are not as firmly localized as in diamond.

explain the relationship between the properties of conductivity and hardness and the structure of ionic, covalent molecular and covalent network structures.

This has already been covered in previous dot points on pages 12, 16-18. Below is a summary:

Property Metallic Crystal Ionic Crystal Covalent Network Crystal

Covalent molecular crystal

Chemical Bonding Metallic Ionic Covalent Covalent

Melting Point High High Very high LowElectrical Conductivity

Solid: highLiquid: high

Solid: nilLiquid: high

- -

Other Properties MalleableDuctileLustrous

HardBrittle

Very HardBrittle

Soft, brittle

Examples CopperAluminium

Sodium ChlorideZinc Oxide

Silicon dioxideSilicon carbide

IceSucrose

identify data sources, gather, process and analyse information from secondary sources to identify the industrial separation processes used on a mixture obtained from the biosphere, lithosphere, hydrosphere or atmosphere and use the evidence available to:

- identify the properties of the mixture used in its separation - identify the products of separation and their uses - discuss issues associated with wastes from the processes used

Fractional distillation is used to separate the components of crude oil. Crude oil is separated into refinery gas, petrol, naphtha, kerosene, diesel, oils and bitumen. The main property used to separate these components is their boiling points.

20

Modern separation involves piping crude oil through hot furnaces. It is hot at the bottom and cool at the top. The crude oil separates into fractions according to weight and boiling point. The lightest fractions which include petrol and LPG, vaporize and rise to the top. Heavier liquids (with higher boiling points) separate lower down.

Products retrieved after the separation include:

- Refinery gas: Bottled gas, fuels- Petrol: Fuel for cars- Naphtha: Raw materials for chemicals and products (eg. Plastic)- Diesel: Fuel for cars- Kerosene: Fuel for aeroplanes- Bitumen: Road surfacing- Oils: Lubricants/grease, also fuel for power stations

Issues associated with wastes include:

- Produced waters, drilling muds and drilling cuttings, as well as discharges of storage displacement are the source of regular and long term impacts of the industry on the marine environment and also in local swamps and land based environments.

- Air and Water pollution. Many oil refineries produce wastes that if released into the air or water can be detrimental to local ecosystems. Refineries must store these wastes onsite, treat them and dispose of them appropriately. However, on the rare occasion, these wastes leak into the environment causing widespread disaster.

analyse information by constructing or using models showing the structure of metals, ionic compounds and covalent compounds

Covalent Network – Strong Lattice structure. This indicates that there is strong intermolecular bonds, giving very high melting and boiling points as well as making the substance hard and brittle (since distortion will break bonds and cause repulsion). There are also strong intramolecular bonds (covalent). They are also non-conductors in any

21

state as there are no free moving electrons, everything is tightly bound in the lattice. They are also insoluble in water.

Covalent Molecular – Separate Molecular structure, all electrons are localized to individual molecules and are not free, therefore not electrical or heat conductivity in any state (unless the substance reacts in water to produce ions). They have strong intramolecular bonds but weak intermolecular bonds which indicate low melting and boiling points and also make them soft solids, liquids or gases.

Ionic – Ions are tightly bound in lattice, therefore non-conductor in solid state. However in molten state the ions are able to move which allows for electrical/heat conductivity. They have a strong lattical structure which indicates strong intermolecular bonds which means high melting and boiling points. This also indicates that the substances are hard. The lattice structure also shows that the substance is brittle because distortion will cause repulsion in like charges causing it to break.

Metallic – Electrical conductors in both solid and liquid form as there are free moving de-localized electrons. This also shows that the substance is malleable and ductile because distortion will cause layers of ions to fall over one another but as the electrons are delocalised they will keep the ions together (there will be no repulsion in like charges). High melting and boiling points due to the lattice structure (strong intermolecular bonds). Also lustrous because the de-localized electrons result in the reflection of light. Finally, the substance is dense due the ions tightly packed together in the lattice. choose resources and process

information from secondary sources to construct and discuss the limitations of

models of ionic lattices, covalent molecules and covalent and metallic lattices

This model is of a metallic substance

Advantages – shows lattice structure which indicates to us that it must be hard as well as have high mp, bp. Strong electrostatic attraction shows us that it will be able to change shape (malleable + ductile).

Limitations – Doesn’t show sea of delocalised electrons which doesn’t tell us that it is a good heat and electrical conductor. Also since it doesn’t show us those electrons, we cannot tell that it is lustrous.

22

Na + Cl - This is a model of an ionic substance

Advantages – Shows us the simplest ration of the elements, which indicates to us that there is one sodium atom per one chlorine. Also shows us the respective charges of each of the ions in the substance, this indicates to us that it is an ionic bond due to the electrostatic bonding.

Limitations – Doesn’t show us the actual lattice structure of the substance, rather shows it as an individual molecule, which it is not. Also doesn’t show electrical conductivity in molten state.

This is also a model of an ionic substance.

Advantages – Shows us the lattice structure of an ionic substance. Shows us the charges of each ion, shows us the electrostatic bonding, shows us the ratio of ions present in the substance, shows us that it will not conduct electricity in solid state as all the ions are tightly packed in the lattice. Also since lattice (high mp, bp)

Limitations – Doesn’t show us that it will conduct electricity in molten state (when the ions are free to move).

NOTE: In order to answer any question that tells you to identify the advantages/ disadvantages/ limitations etc of a model:

First identify what type of substance it is (eg ionic, covalent molecular etc.).

Then recall the properties of those substances and see if the model shows those properties. If it does it is an advantage, if it doesn’t it is a limitation.

List of Polyatomic ions (Radicals)

+1 -1 -2 -3NH4+ ammonium

Hydronium H3O+

OH- hydroxide

NO3- nitrate

ClO3- chlorate

MnO4-

permanganate

SiO32- silicate

C22- carbide

O22- peroxide

S22- disulfide

PO43- phosphate

PO33- phosphite

23

Cyanide CN-

Bicarbonate HCO3-

Hydrogen Sulfate HSO4-

Carbonate CO32-

Chromate CrO42-

Hydrogen Phosphate HPO42

Sulfate SO42-

Hydroxide OH-

Sulfite SO32-

Nitrate NO3-

Nitrite NO2-

HCO3- hydrogen carbonate

HSO3- hydrogen sulfite

CH3COOH- acetate

24